Shelf



FIG. 1 is a perspective view of a shelf showing our new design;

FIG. 2 is an end view thereof, the opposite end being a mirror image of the side shown;

FIG. 3 is a top plan view thereof; and,

FIG. 4 is front view thereof, the opposite side being a mirror image of the side shown. 

The ornamental design for a shelf, as shown and described. 